The present invention relates to solar energy systems and in particular to collectors for the heating of air and simultaneous production of electric power through photovoltaic effect.
The production of direct current electric power from suitable photovoltaic solar cells is a well known art. For example, the use of silicon cells for producing electric power for space vehicles has been very successful. One commercial system involves the use of a thin film of such high photo active material as copper-sulphide or cadmium-sulphide deposited on the lower inside surface of a hermetically sealed, double panel glass panel. When such a panel intercepts sunlight, the photovoltaic film is able to convert as much as 7% of the sunlight falling upon the panel into useful electric power.
Solar cells also convert sunlight into heat, as well as electric energy. Therefore, heat as well as electric energy can be a useful product from a system of one or more solar cells.
It is well known that the efficiency of electric power production for almost all types of photovoltaic electric cells is increased by keeping the temperature of the photovoltaic material as low as possible. On the other hand, in cases in which hot air is to be obtained for such applications as heating domestic hot water and space heating of buildings, it is desirable to produce the air at a reasonably high temperature such as 160.degree. or even 200.degree. F. In general these two criteria are opposites of each other and there is not known any successful system in which the optimum production of electricity and heat are simultaneously obtained.
In conventional cases in which the heat by-product from solar cells would be utilized to heat air, the cells would comprise the hot sunlit cover of a suitable collection box and cold air would usually be allowed to enter the box at one end and heated air would leave the other end, passing through the spaces between the individual solar cells. In the use of such a box, heat would be transferred to the air inside mostly by radiation from the hot underside of the cells, and a large temperature difference would exist between the cooler air temperature in the box and the hot backside of the solar cells because of poor heat transfer between the backside and the air in the box. All of this results in an excessively high temperature for the solar cells and above all would be contrary to efficient conversion of sunlight into electricity.
It is the object of the present invention to provide a combined solar air heating collector and solar energy electric power cell which primarily converts a maximum percentage of the intercepted sunlight energy into useful electric power and at the same time produces as a by-product the hottest air possible.
It is a further object of the present invention to increase as much as possible the efficiency of transferring heat from a solar electric power cell to a stream of flowing air, and to lower as much as possible the capital cost per square foot of fabricated material which is used to augment efficient heat transfer from a solar cell to flowing air. It is another object of the present invention to produce the hottest air possible with photovoltaic cells while still maintaining an acceptably low temperature of the photovoltaic material within the cell, as well as to effect the most efficient low cost cooling of photovoltaic electric cells.
These objects, together with other objects and advantages of the present invention will be apparent from the following disclosure.